Turnstile antenna



y 1947. R, c. MOORE 2,420,967

TURNSTILE ANTENNA Filed Dec. 30, 1944 Patented May 20, 1947 2,420,967TURNSTILE ANTENNA Robert C. Moore, Philadelphia, Pa., assignor, by toPhilco Corporation, Philadelphia, Pa., a corporation of Pennsylmesneassignments,

vania Application December 30, 1944, Serial No. 570,675

9 Claims.

This invention relates to an electrical apparatus and particularly anantenna system. In particular, the invention relates to a turn-stileantenna system for ultra-high frequencies whereby a more compact anddesirable system is provided. As is well known, a turn-stile type ofantenna system may include one or more banks or bays of a group of twoor four antennas. A group of four antennas for a bay may be disposed ina generally horizontal plane witha 90 degree geometrical and electricalangle between adjacent antennas to obtain a generally circular radiationpattern in azimuth. Two superposed groups of two antennas for a bay mayalso be provided. Such turnstile antenna arrays are used to some extentat high frequencies for frequency modulation transmission, sometelevision work, and similar purposes.

In order to feed properly the four antennas of a turn-stile group, it isnecessary to advance or retard the phase of the current in each memherof the group by 90 degrees progressively. Such a requirement hashitherto made it necessary to provide half wave stubs for obtaining thenecessary phase correction. The use of such stubs in an antenna systemof this character is objectionable for various reasons. For one thing,such antenna systems may be exposed to adverse weather where sleet andsnow may collect. For another thing, the use of shorting stubs resultsin a mechanical system susceptible to vibrations and having sometendency to modulate transmission or reception of energy. In additionthereto, the use of half wave stubs creates additional tuning problems.

In accordance with the invention herein, a turnstile antenna system ofthe type having four arms to a bay is provided. This system ismechanically and electrically simple and efiicient. The mechanicalsimplicity results in a streamlined structure which may be importantwhen I used at the top of a high building or in an exposed position.Electrically, the invention provides an antenna system which canaccommodate an unusually broad range of frequencies.

In many instances, such as in television work, a wide range offrequencies must be used so that the band width of the system must ofnecessity be substantial. Considerable difiiculty is experienced indesigning an antenna system having a substantial band width at highfrequencies due to the extremely sharp resonance characteristics ofcircuits at such frequencies.

In order to widen the band width of an antenna system, it has hithertobeen the practice to decrease the ratio of length to diameter of theradiating elements. However, this alters the radiation resistance andinput impedance of the system in cases where it is undesired. By virtueof the invention herein, the antenna system as a whole presents asubstantially pure resistance to the feed lines and presents asubstantially constant impedance over a wide band.

The usual type of dipole customary in tumstile systems inherently has anarrow band width and thus cannot present a substantially constantimpedance over any substantial band width. Because of this, the use ofsuch antenna systems in television work has been greatly restricted.

Referring to the drawing:

Figure 1 is a schematic circuit diagram of a system embodying thisinvention.

Figure 2 is a diagrammatic illustration of an antenna system embodyingthe present invention.

Figure 3 is an elevation with certain parts broken away showing apractical antenna system embodying the invention.

Figure 4 is a section on 4-6 of Figure 3.

Referring first to Figure 1, a transmission line consisting ofconductors l and 2 may be supplied with energy at high frequency eitherfrom a suitable transmitter or may be connected to suppl energy to asuitable receiver, depending upon whether the antenna system is to beused for transmission or reception. If wires I and 2 are formed as anopen line, it is understood that the spacing between them must be smallin comparison to the wave length so that radiation from the linewill besuppressed. Actually, wires l and 2 are merely symbolic and. thetransmission line which they represent may be an open line, a coaxialcable, as shown in Figures 3 and 4, or a wave guide. Inasmuch asfeedingfrom transmission lines is highly developed and well known in the art,the substitution of one form of line for another may be efiectedreadily.

Conductor i may have connected thereto terminal d of a radiating antennaunit generally designated as 5 and consisting of an antenna radiatingarm 6 and inductive reactance I. Inductive reactance I may in itsphysical form be incorporated in as part of radiating arm 6 or, ifdesired, may be separate and associated with radiating arm 6. Conductorl is also connected to terminal 8 of a radiating unit 9 consisting of anantenna arm l0 and capacitive reactance H. As is the case with unit 5,unit 9 may have the reactance and radiating arm all together in onephysical structure or be separate.

Conductor 2 is similarly connected to terminal I2 of unit I3 havingradiating antenna arm I4 and inductive reactance I5. Conductor 2 is alsoconnected to terminal I6 of unit I! having radiating arm I8 andcapacitive reactance I9.

It is understood that terminals 4 and 8 are fed in phase and thatterminals I2 and I6 are similarly fed in phase. The reactance in eacharm is approximately equal to the radiation resistance of that arm atthe frequency of operation, particularly the center of the band. Thus asubstantially 45 degree phase angle between resistance and impedance isprovided. In the case of an inductive reactance, the voltage will leadthe current by 45 degrees. With capacitive reactance, the voltage willlag the current by 45 degrees.

The feed for units and 9 is 180 degrees out of phase with the feed forunits I3 and I1. Thus antenna radiating arms III and I8 will beoppositely poled and constitute the stubs of a dipole unit. The same istrue of radiating arms 6 and I4. By virtue of the magnitude of reactanceand radiation resistance, there will be a ninety degree diilerence inphase between the currents in the radiating arms progressively around anantenna bay. Thus dipole unit Ill and ill will have a phase differenceof ninety degrees as far as radiation is concerned with respect todipole units 6 and I4. To be more specific, the current in dipole unit I6 and i6 leads the voltage by fortyfive degrees whereas the current indipole unit 6 and I4 lags the voltage by forty-five degrees. Thus aturnstile action results and radiation is provided.

In order to embody the antenna system of Figure l in a practicalstructure, it is preferred to utilize as radiating elements half dipolestubs as shown in Figure 2. Thus antenna arm 6, which has inductivereactance, may consist of metal tube 20. Within tube 20, centerconductor 2| is provided, this center conductor being electricallyjoined to inside surface 22 of tube 20 by metal shorting disc 23.Shorting disc 23 may be provided with spring fingers 24 and 25 forengaging inner surface 22 of cylinder 26 and central conductor 2| (SeeFigures 3 and 4.)

It is understood that cylinder 20 is closed at the outer end. Theposition of disc 23 along conductor 2| inside of cylinder 20 may bedetermined by calibration or experiment and should be so chosen as toproduce desired inductive reactance.

The length of cylinder 20 will also be a factor in this. If desired,cylinder 26 may have a generally ovoid shape on the outside to controlthe band response characteristics. The major axis of the ovoid wouldnaturally be coincident with the inside cylindrical axis of wall 22.

Capacitive antenna arm I 0 has cylinder 30 of the same generalconstruction as cylinder 26. Within cylinder 30, center conductor 3| maybe provided and this may be maintained centered within cylinder 30 bymeans of suitable insulating beads 32 disposed in a manner to avoidundue reflection. If desired, the inside of cylinder 36 may be filledwith dielectric such as polystyrene and conductor 3| disposed therein.Antenna arms I4 and I8 resemble antenna arms 6 and II! respectively intheir physical construction having center wires 33 and 34 inside ofcylinders 35 and 36.

To support the structure, standard 31 may be provided. This standard maybe made of metal pipe and may have insulating bushings 38 from whicheach antenna unit may be supported. The

insulating bushings may be supported in the pipe in any suitable fashionso that sumclent mechanical strength as well as insulation is provided.It is preferred to have the diameter of the standard as small aspossible to reduce to a minimum the amount of metal and dielectric inthe vicinity of the radiators. The actual diameter or size of pipe isnot critical. By virtue of small size of pipe and dielectric, theradiation pattern will be less afiected.

Bushings 38 may have apertures 4i into which each antenna arm unit isrigidly secured. A second series of apertures 42 may be provided foranother bay, the two bays being preferably one half wave length apart.

While various means for feeding the antenna may be provided such as openline, balanced coaxial cables or even wave guide, a simple means usingone coaxial cable is herewith shown. A coaxial cable ordinarily has theoutside of the outer cable at groundpotential and the two surfaces atradio frequency potential are not balanced with respect to ground. Asused\ herein, however, it is desirable that the feed lines connected tothe antenna arms be balanced to ground so that the antenna armsthemselves will not be at different potentials with respect to ground.

In order to obtain a coaxial cable section that is balanced to ground, abalancing sleeve is used. Thus, the coaxial feed cable may have outerconductor 44 and inner conductor 45 spaced in a manner well known in theart, and having a predetermined ratio of diameters to provide a desiredcharacteristic impedance. Outer conductor 44 is provided with sleeve 46,this sleeve having a length substantially a quarter wave along its ax s.It is understood that bottom 41 of sleeve 46 is joined to outerconductor 44 so that an annular cup around outer conductor 44 is formed.Sleeve 45 extends upwardly toward the antenna arms and terminates infree edge 48.

Beyond sleeve 46, an open line may be used. However, a coaxial line isshown. The coaxial line extends beyond balancing sleeve 46 and, sincethe opposed conducting surfaces are balanced to ground, connections tothe antenna arms may be made thereto. Thus, at point 50 on centerconductor 45, leads 2| and 3i for radiating pipe members 20 and 30 maybe connected. These leads pass through apertures in outer conductor 44.At point 5| on the inside surface of outer conductor 44, this pointbeing opposite in polarity to point 50, connections to conductors 33 and34 of cylinders 35 and 36 are made.

A half wave length beyond the region in standard 31' where the first bayoccurs, a second bay may be provided. This second bay may consist offour arms symmetrically disposed and aligned with the four arms of thelower bay. These four arms are numbered I20, I30, I35 and I36 respectively. The corresponding parts in the two bays are similarly numberedwith the difference of one hundred between the corresponding numbers,

For certain purposes, it is desirable that the corresponding arms beconnected at points of opposite polarity, the bays being separated byone-half wave length. Thus arms I20 and I30 may have their centerconductors HI and BI connected to point I5I on the inside surface ofouter conductor 44. In the case Where the center conductors of theantenna arm units connect to the inside surface of the outer conductor.such wires may pass through suitable apertures in outer conductor 44 andbe soldered or joined thereto in a manner well known in the art.Radiating arms I35 and I36 have their center It is understoodthatadditional bays may be' provided and, in fact, as many may be providedas may be deemed necessary. The spacin between adjacent bays may be awave length if desired, in which case noreversal of polarity ofcorresponding superposed arms will be necessary. However, it ispreferred to have adjacent bays separated by a distance of one-half wavelength, as the radiation pattern appears to be more desirable.

Since bays are separated by a distance of onehalf or in some instancesone whole wave length, it is clear that all of the bays as seen at theinput to the entire system are effectively in parallel. In someinstances, it is possible that the wide frequency band over which thesystem is adapted to operate may result in some mismatching. Thus, it isclear that a separation of one-half a wave length between adjacent baysis true for only a narrow band of frequencies. Where the desired bandwidth is substantial, the separation between adjacent bays mayeffectively be somewhat less or greater than one-half a wave length. Insuch case, some matching for the mid frequency is desirable, so thatsatisfactory operation over the entire frequency range will be had. Incertain instances, it may be desirable to provide separate feed lines toeach bay.

The outer radiating surface of each of the radiating arms is preferablyof the order of one quarter wave length. The exact length is a complexfunction involvin among other things the ratio of length to diameter,proximity of other arms, shape of cylinder arms and other factors. Inthe case where each arm has a transmission line section built in, asshown herein, it'is clear that each arm has a transformer therein forimparting a predetermined magnitude of reactance.

It is possible to design the length of each of the radiating arms sothat the radiating surface has a. reactive component. In that particularcase, the transmission line section within each arm would be entirelyeliminated and a direct connection from the feed line to the radiatingsurface would be provided. It is also possible to have some reactance ineach radiating arm and supplement this with a transmission line sectionwithin each arm so that the total reactance would combine to provide adesired magnitude.

It is understood that the diameter of the inner and outer conductor ofeach transmission line section within a radiating arm are properlyproportioned to give a desired characteristic impedance as seen from thesupply cable. Naturally, the thickness of each of the cylinder wallsmaking up a radiating arm may be varied so that the ratio of diametersof the coaxial transmission cable within a radiating arm is independentof the dimensions of the arm itself. By properdesign, the combination ofthe four arms of each bay may present a substantially pure resistiveload as seen from the supply cable. Thus accurate matching for maximumenergy transfer may be obtained.

The standard may terminate in an end cap as shown. Since the feed issubstantially nonresonant, and since substantially perfect matching ispresumed, it is clear that no special termination for the feed line orstandard is necessary. The fact that the entire system presents asubstantially pure resistive load is desirable,

particularly in the event that long open line feeders are used. In suchcase, substantially nonresonant lines may be used, and the variation inthe length of line Or variation in frequency will have little or noeffect. A construction of this character may thus be pre-fabricated andpretuned.

It is understood that the use of the terms capacitive and inductivereactance herein refers to the phase angle between current and voltage.At the frequencies involved, the ordinary concept of inductance andcapacitance is unsatisfactory. Thus it is well known that the samephysical structure having a. diiferent electrical length may go from aninductive reactance through substantially pure resistance to acapacitive reactance.

What is claimed is:

1. A turnstile type of antenna comprising a support, four arms radiatingfrom said support with said arms generally lying in a plane and havingan angle of ninety degrees between adjacent arms, each arm comprising ametal member having a hollow interior, a conductor disposed within saidinterior and spaced therefrom, one pair of diametrically opposed armsforming a dipole and having a shorting member for each arm between thecentral conductor and the interior of said arm, the remaining two armsforming a dipole and having capacitive connections to their conductors,each of said arms having the interior functioning as a phasing sleeve,said arms and sleeves being so proportioned as to provide for aninety-degree difierence in phase between adjacent arms progressivelyaround the four arms, and means for feeding the central conductors oftwo adjacent arms in phase and for feeding the central conductors of theremaining arms in opposed phase.

2. The system of claim 1 wherein said arms have the interior phasingsleeves so proportioned and so long that the pair having shortingmembers have inductive reactance and the open pair have capacitivereactance.

3. The system of claim 1 wherein said dipole arms are all the samelength with each arm being substantially a quarter wave length long andwherein the phasing sleeves within one pair of dipole arms are soproportioned as to present an inductive reactance and wherein thephasing sleeves within the remaining dipole arms are so proportioned asto present a capacitive reactance, the inductive and capacitivereactances having a ninety-degree phase difference between adjacentarms.

4. A turnstile type of antenna comprising an insulating standard, atleast one bay of antenna arms radiating from said standard with adjacentarms being electrically and geometrically ninety degrees apart, each armincluding a metallic cylinder having an exterior radiating surface andhaving a cylindrical surface formed on the inside, opposing arms forminga dipole, each of said arms having a centrally disposed conductor withinthe interior thereof, the arms of one dipole having a shorting memberwithin each arm between the center conductor and the interior metalsurface, the arms of the remaining dipole having capacitive connectionbetween each arm and the surrounding metallic surface, at least onetransmission system within said standard, metallic connections betweensaid transmission line to the center conductors of said arms, twoadjacent arms being fed in phase and the remaining adjacent arms beingfed in phase but oppositely poled, the center conductor and insidecylindrical surface for each arm forming a phase sleeve having apredetermined length and dimension to provide a phase diiference ofninety degrees between the two dipoles.

5. The system of claim 4 wherein each of said arms is substantially aquarter wave length long.

6. The system of claim 4 wherein each arm is substantially a quarterwave length long and wherein the phasing sleeves having metallicconnection between the center conductor and surrounding cylinder Wallprovide an inductive reactance and wherein the remaining phasing sleevesprovide a capacitive reactance.

'7. The system of claim 4 wherein a pair of superposed bays spacedone-half wave length apart are provided, the corresponding arms of eachbay being in the same vertical plane with corresponding arms being fed180 degrees out of phase.

8. A turnstile antenna for use at high carrier frequencies, said antennacomprising four-halfdipole radiator elements extending outwardly at 90degree intervals from a common center, each one of said radiatorelements comprising a hollow cylindrical conducting member, each pair ofoppositely disposed radiator elements comprising a dipole element, eachradiator element having an inner coaxial conductor extending part Wayonly into said radiator element from the inner end thereof, the outerends of the coaxial conductors in only one of said dipoles beingshuntedto the inner surface of the corresponding radiator elementsthrough a path having low impedance at said carrier frequencies, meansfor energizing said dipoles in parallel from a common source of highfrequency carrier wave energy, said means comprising connections betweensaid source and the inner ends of said coaxial conductors, the length ofsaid coaxial conductors being such that a substantially degree phaseshift is eiiected between the currents in said dipoles.

9. A turnstile antenna for use at high carrier frequencies, said antennacomprising four halfdipole radiator elements disposed in a common planeand extending radially outward at 90 degree intervals from a commoncenter, each one of said radiator elements comprising a hollowcylindrical conducting member closed at the outer end and open at theinner end thereof, each pair of oppositely disposed radiator elementsconstituting a dipole, each radiator element having an inner coaxialconductor extending part way only into said radiator element from theinner end thereof, the outer ends of the coaxial conductors in only oneof said dipoles being connected directly to the inner surface of theassociated radiator elements through a path having low impedance at saidcarrier frequencies, means for energizing said dipoles in parallel froma common source of high frequency carrier wave energy, said meanscomprising connections between said source and the inner ends of saidcoaxial conductors, the length of said coaxial conductors being suchthat a substantially 90 degree phase shift is effected between thevoltages applied to said dipoles.

ROBERT C. MOORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,245,693 Lindenblad June 17,1941 2,275 030 Epstein Mar. 3, 1942 2,297,329 Scheldorf Sept. 29, 1942

